The term "stereolithography" denotes a process for the production of complex solid 3-dimensional objects by curing successive thin layers of photocurable liquid composition using a computer controlled laser to affect patterned photocuring of the liquid surface. The technique is described in detail in Murphy, et al, "Reduced Distortion in Optical Free Form Fabrications with UV Lasers", Radiation Curing, Feb-May 1989, pp. 3-7; Chemical Week, Sep. 9, 1987, pp. 24-25; and in U.S. Pat. Nos. 4,575,330; 4,801,447; 4,929,402; and 4,752,498, all incorporated herein by reference.
Heretofore it has been conventional to use various acrylic ester monomers as the photocurable liquids for stereolithography because of their fast UV response time and lack of curing outside the irradiation boundary. However, acrylic esters have very high shrinkage upon curing which has severely restricted to practical utility of the stereolithography technique. As successive layers are built up, complex objects are distorted by shrinkage differences between portions of the object.
While photocurable resin systems having lower shrinkage, such as photocurable epoxy formulations, are well known such systems were generally considered to have lower UV response and/or greater potential for continued curing outside the irradiation boundaries than acrylic monomers. Consequently, such systems have heretofore been rejected as undesirable for stereolithography applications.
In U.S. Pat. No. 4,808,638 there are described photocurable thiolene compositions comprising a norbornene functional resin, a polythiol and a free radical photoinitiator. Further description of this system may be found in Jacobine et al, Proceedings of ACS Division of Polymeric Materials: Science and Engineering, Vol. 60, pp. 211-216 (1989).